Fighting the Avian Leukosis Virus through Genome Modification

The avian leukosis virus subgroup J (ALV-J) has plagued the poultry industry since being recognized about 30 years ago. The economic hardships caused by decreases in poultry yield makes developing resistance mechanisms a topic of interest. Recently, a team led by Hong Jo Lee from Seoul National University decided to take the novel approach of editing the chicken genome in order to induce ALV-J resistance. They used CRISPR-Cas9, a classic tool used to edit the genome through excision and insertion by vectors.

The team targeted the Na+/H+ exchange 1 (chNHE1) receptor on fibroblasts, a type of connective tissue, which is specifically required for ALV-J to gain entry to the host cell. Four different types of vectors were used as experimental groups; two had puromycin resistance while the other two featured neomycin resistance. Both puromycin and neomycin are antibiotics, however, puromycin works inhibits protein synthesis while neuomycin prevents bacterial growth. Cells were infected using an infectious ALV-J vector with green fluorescent protein (GFP) expressing capabilities. Untreated and infected wild type fibroblasts were used with control. The response from virus challenge was telling. Cells with premature stop codons in the chNHE1 transcript demonstrated almost no GFP expression, indicating complete resistance. Cells that were tailored with a tryptophan deletion at position 38 (Trp38) showed significantly less GFP expression than cells without the deletion. This indicates that the tryptophan deletion may prove to reduce the level of infection. Techniques in bioinformatics were then utilized to discover that the localized region with Trp38 represented a major binding interface for ALV-J. Thus, removing Trp38 in tandem with other important amino acid sequences form crucial conformation structures could prevent ALV-J infection in poultry.

The development of a system to combat avian diseases requires further research, as the chNHE1 receptor is highly conserved in chickens. However, the newly developed, precise CRISPR-Cas9 technique appears to be a promising solution.